Any doubts about whose interests are served by ISIL (ISIS, Daesh, Islamic State) in Syria have been eliminated. Saudi Arabia, Bahrain and the United Arab Emirates have all stated their willingness to send ground forces to Syria to fight ISIL as part of a global coalition led by the United States.

Syria and Iran have reacted with menacing negativity. So much for the fiction that Iran, its Syrian client, and, for that matter, Russia see ISIL in Syria as an enemy. For all three it is a gift that keeps on giving.

For Syrian President Bashar al-Assad, ISIL is the evil foil serving the purpose of making him and his regime look good by comparison. As qualified as he is for war crimes prosecution, he has avoided public beheadings and burnings.

For the Syrian regime and the self-proclaimed ISIL "caliph" Abu Bakr al-Baghdadi, the relationship is largely one of live-and-let live. When ISIL sees something it wants — an airbase filled with weaponry, a city featuring priceless antiquities, or an oil field — it sweeps away Assad regime forces in its path.

But the two supposed enemies really have much in common. Each seeks militarily to eliminate all Syrian nationalist alternatives to the other. Each sees value — Assad for a ticket back to polite society, Baghdadi for recruiting worldwide in Sunni Muslim communities — in the other being one of the two only political figures left standing in Syria.

ISIL’s value to the Assad regime skyrocketed on Sept. 30, 2015, when Russia intervened militarily. Moscow proclaimed it was deploying combat aircraft to Syria to fight ISIL. It then proceeded to do almost anything but. Aside from an occasional bombing run for appearances sake, or to help out a regime unit sitting atop something desired by ISIL, Russia’s bombing campaign is clearly designed to help the Assad regime, and by extension ISIL, eliminate Syrian nationalist alternatives to Assad family rule.

Washington tried to play diplomatic judo with Russia’s intervention. With a straight face, Secretary of State John Kerry tried to codify Moscow’s anti-ISIL pretension. Characterizing ISIL as the common enemy of the civilized world, he devised a diplomatic process he hoped would ultimately sideline Bashar al-Assad –a person neck-deep in war crimes and crimes against humanity–for the sake of a unified Syrian ground force (Army and rebels together) against ISIL. 

Kerry's initiative has fallen on hard times. A Geneva peace conference was convened and almost instantly suspended. Russia, notwithstanding its status as "co-convener" of the diplomatic initiative, escalated its pro-regime air campaign: not against ISIL, but against Syrian rebels holding parts of Aleppo. Targeted Russian airstrikes against civilian residential areas combined with fears of regime ground forces surrounding the city have produced yet another wave of terrified refugees headed for NATO's southern flank: Turkey.

Despite Notwithstanding the combined effects of Russian aircraft, the Syrian Army and Iranian-assembled foreign fighter militias against Syrian rebels in western Syria, three Gulf states in succession announced their readiness to dispatch ground forces to eastern Syria to fight neither the regime, nor Russia, nor Iran, but ISIL. US Defense Secretary of Defense Ash Carter reacted quickly: "That kind of news is very welcome."

Indeed it is. What the war against ISIL in Syria has lacked is a ground combat component large enough and professional enough to close with and kill ISIL. Air attacks have had some success. A Kurdish militia seeking to establish an autonomous zone along the border with Turkey has done some good. Much more, however, would be required to eliminate ISIL’s safe haven in Syria. ; an outcome that would hasten coalition victory in Iraq as well.

Is the Gulf offer real? Do the three states have ground force capabilities that can contribute to a decisive campaign against ISIL in Syria? These questions are, no doubt, being probed carefully by DoD.

What is on the record, however, is Russian behavior and regime and Iranian reactions. According to al-Assad's foreign minister, any such anti-ISIL coalition "will be considered aggression," and its participants "will return home in wooden coffins."

The leader of the Iranian Revolutionary Guard Corps opined that if the Saudis "send troops, they would be definitely defeated ... it would be suicide." So much for ISIL the enemy.

John Kerry’s diplomacy and good intentions notwithstanding, what we are seeing in Syria is a collaborative military effort embracing Russia, Iran, ISIL and the Assad regime. If all four succeed in eliminating Syrian nationalist alternatives to al-Assad and ISIL, will Assad and his allies then turn against the "caliph?" Or will Syria slip into an uneasy, unstable partition between two violently criminal entities?

Either way Moscow hopes to force Washington to crawl back into the good graces of its Syrian client: a prospective victory for Russia and humiliation for the United States.

The fiction of ISIL as a common enemy had diplomatic utility for John Kerry. Russian actions and the reactions of Iran and the Assad regime to the Gulf ground force offer have killed it. Facts, now being created by Russia, must, for better or worse, govern Syria-and ISIL-related policy.

Ambassador Frederic C. Hof is an Atlantic Council Senior Fellow, a Vietnam veteran, and a former State Department official.

More In Commentary